Methods are disclosed for reducing compounds of iron to iron by reacting the ores with hydrocarbons in the absence of oxygen.
In the prior art iron ores, principally hematite containing Fe.sub.2 O.sub.3, magnetite containing Fe.sub.3 O.sub.4, siderite containing FeCO.sub.3 and limonite containing Fe.sub.2 O.sub.3.3H.sub.2 O, are reduced in a blast furnace with metallurgical coke as fuel, limestone as a flux and a blast of air. Oxygen in the blast reacts with carbon in the coke to deliver heat and form carbon dioxide. The carbon dioxide reacts with carbon to form carbon monoxide which reduces the iron compounds to iron, and the furnace delivers heated carbon monoxide, carbon dioxide, nitrogen and water vapor. Silica present in the ores reacts with calcium carbonate to form a liquid slag. Iron and slag may be tapped separately from the furnace. The exhaust gas may be used to heat the air blast, to provide heat for other uses and to supply flammable gas. Smelting by direct reduction and by the use of other fuels including hydrocarbons with oxygen added to also known.
In operation, preparation and handling of coke, operation and maintenance of the air blast, and effective utilization of furnace gases require substantial amounts of skilled labor.
Excessive consumption of fuel and high labor costs mean that blast furnace operation is recognized as unsatisfactory. This result arises as a usable form of gaseous carbon does not occur, and the expedient chosen is to use carbon monoxide.
In the invention a furnace is charged with iron ore which is traversed with a rapid current of hydrocarbon gas free from oxygen and compounds containing oxygen, except carbon dioxide. The reaction of some hydrocarbons with iron ores is exothermic, so that additional heat may not be required. In other cases the hydrocarbon is preheated. The cost of fuel, hydrocarbon and labor may be substantially less than an equally productive blast furnace operation.
A usual impurity in iron ores is silica. In the invention the silica and the iron compounds may be separated by mechanical means at relatively low cost, before exposure to the hydrocarbon, because of the substantial difference of density between the iron compounds and silica.